Methods and means for casing, perforation and sand-screen evaluation using backscattered x-ray radiation in a wellbore environment

ABSTRACT

An x-ray-based cased wellbore environment imaging tool is provided, the tool including at least an x-ray source; a radiation shield to define the output form of the produced x-rays; a direction controllable two-dimensional per-pixel collimated imaging detector array; sonde-dependent electronics; and a plurality of tool logic electronics and PSUs. A method of using an x-ray-based cased wellbore environment imaging tool to monitor and determine the integrity of materials within wellbore environments is also provided, the method including at least: producing x-rays in a shaped output; measuring the intensity of backscatter x-rays returning from materials surrounding the wellbore; controlling two-dimensional per-pixel collimated imaging detector arrays; and converting image data from said detectors into consolidated images of the wellbore materials.

TECHNICAL FIELD

The present invention relates generally to methods and means formonitoring and determining casing and sand-screen integrity withinwellbore environments.

BACKGROUND

Within the oil & gas industry, it is very important to accurately gaugethe quality of casings. The industry currently employs various methodsfor the verification of the quality of the casing. Typically, calipersor cameras are employed to determine whether the casing/tubing iscylindrical and or not-corroded. However, cameras require the wellboreto contain optically clear fluids; otherwise, they are incapable ofdistinguishing features within the fluid/borehole. More recently,ultrasonic tools are run within the well in an attempt to image thecasing/tubing, or elements outside of the tubing, such as the parts of adownhole safety valve. However, ultrasonic tools are model dependent, soprior knowledge of the precise makeup and status of the well istypically required for the ultrasound data to be compared against.

No viable technologies are currently available which use a method ormeans to employ a combination of collimators, located cylindricallyaround an X-ray source, located within a non-paddedconcentrically-located borehole logging tool, together with a single orplurality of rotatable two dimensional per-pixel collimated imagingdetector array(s) to also be used as the primary imaging detector(s), toproduce complete backscatter images of the casing/tubing.

Prior art teaches a variety of techniques that use x-rays or otherradiant energy to inspect or obtain information about the structureswithin or surrounding the borehole of a water, oil or gas well, yet noneteach a method or system to use first order detectors (which aretypically used to compensate for mud-cake/fluid variations) to create aphotograph-like image of the casing itself.

U.S. Pat. No. 7,675,029 to Teague et al. teaches an apparatus whereinthe measurement of x-ray backscattered photons from any horizontalsurface inside of a borehole admits to two-dimensional imagingtechniques.

U.S. Pat. No. 8,481,919 to Teague teaches a method of producingCompton-spectrum radiation in a borehole without the use of radioactiveisotopes. The reference further teaches rotating collimators around afixed source installed internally to the apparatus but does not havesolid-state detectors with collimators. It further teaches the use ofconical and radially symmetrical anode arrangements to permit theproduction of panoramic x-ray radiation.

U.S. Pat. No. 7,705,294 to Teague teaches an apparatus that measuresbackscattered x-rays from the inner layers of a borehole in selectedradial directions, with the missing segment data being populated throughmovement of the apparatus through the borehole. The apparatus permitsgeneration of data for a two-dimensional reconstruction of the well orborehole, but the publication does not disclose the necessary geometryfor the illuminating x-ray beam to permit discrimination of the depthfrom which the backscattered photons originated, rather, only thedirection.

U.S. Pat. No. 3,564,251 to Youmans discloses the use of a azimuthallyscanning collimated x-ray beam to produce an attenuated signal at adetector for the purposes of producing a spiral-formed log of the insideof a casing or borehole surface immediately surrounding the tool,effectively embodied as an x-ray caliper. However, the reference failsto teach or suggest a means or method to create a photo-like image,other than a two-dimensional radial plot on an oscilloscope.

U.S. Pat. No. 7,634,059 to Wraight discloses an apparatus that may beused to produce individual two-dimensional x-ray images of the innersurface inside of a borehole using a single pin-hole camera without thetechnical possibility to ascertain the azimuth of the image being taken,so that a tessellation/stitching of multiple images is also notdisclosed.

US2013/0009049 by Smaardyk discloses an apparatus that allowsmeasurement of backscattered x-rays from the inner layers of a borehole.However, the reference fails to disclose a means or method to createphoto-like two dimensional images of the inner surfaces of the casingwhile the tool is being axially moved (‘logged’) through the wellbore sothat a consolidated two-dimensional image of the well casing can beproduced.

U.S. Pat. No. 8,138,471 to Shedlock discloses provides a scanning-beamapparatus based on an x-ray source, a rotatable x-ray beam collimator,and solid-state radiation detectors enabling the imaging of only theinner surfaces of borehole casings and pipelines. However, the referencefails to disclose a means or method to create photo-like two dimensionalimages of the inner surfaces of the casing while the tool is beingaxially moved (‘logged’) through the wellbore so that a consolidatedtwo-dimensional image of the well casing can be produced.

U.S. Pat. No. 5,326,970 to Bayless discloses a tool that attempts tomeasure backscattered x-rays azimuthally in a single direction in orderto measure formation density, with the x-ray source being based on alinear accelerator. However, the reference fails to teach a means ormethod to create photo-like two dimensional images of the inner surfacesof the casing while the tool is being axially moved (‘logged’) throughthe wellbore so that a consolidated two-dimensional image of the wellcasing can be produced. It also fails to teach or suggest a method andmeans that uses a fixed conical/panoramic beam to illuminate the wellcasing, whereas the directional collimation is located at the rotatingdetector.

U.S. Pat. No. 5,081,611 to Homby discloses a method of back projectionto determine acoustic physical parameters of the earth formationlongitudinally along the borehole using a single ultrasonic transducerand a number of receivers, which are distributed along the primary axisof the tool.

U.S. Pat. No. 6,725,161 to Hillis discloses a method of placing atransmitter in a borehole and a receiver on the surface of the earth, ora receiver in a borehole and a transmitter on the surface of the earth,with the aim to determine structural information regarding thegeological materials between the transmitter and receiver.

U.S. Pat. No. 6,876,721 to Siddiqui discloses a method to correlateinformation taken from a core-sample with information from a boreholedensity log. The core-sample information is derived from a CT scan ofthe core-sample, whereby the x-ray source and detectors are located onthe outside of the sample, and thereby configured as anoutside-looking-in arrangement. Various kinds of information from the CTscan such as its bulk density is compared to and correlated with the loginformation.

U.S. Pat. No. 4,464,569 to Flaum discloses a method to determine theelemental composition of earth formations surrounding a well borehole byprocessing the detected neutron capture gamma radiation emanating fromthe earth formation after neutron irradiation of the earth formation bya neutron spectroscopy logging tool.

U.S. Pat. No. 4,433,240 to Seeman discloses a borehole logging tool thatdetects natural radiation from the rock of the formation and logs saidinformation so that it may be represented in an intensity versus depthplot format.

U.S. Pat. No. 3,976,879 to Turcotte discloses a borehole logging toolthat detects and records the backscattered radiation from the formationsurrounding the borehole by means of a pulsed electromagnetic energy orphoton source, so that characteristic information may be represented inan intensity versus depth plot format.

U.S. Pat. No. 8,664,587 to Evans et al. discloses a method and means forcreating azimuthal neutron porosity images in a logging while drillingenvironment. Since bottom hole assembly based systems historicallyrelied upon the rotation of the drill string to assist in theacquisition of azimuthally dependent data, the reference discusses anarrangement of azimuthally static detectors which could be implementedin a modern BHA that does not necessarily rotate with the bit, bysubdividing the neutron detectors into a plurality of azimuthallyarranged detectors which are shielded within a moderator to inferdirectionality to incident neutrons and gamma.

U.S. Pat. No. 9,012,836 to Wilson et al. discloses a method and meansfor creating azimuthal neutron porosity images in a wirelineenvironment. Similar to U.S. Pat. No. 8,664,587, the reference discussesan arrangement of azimuthally static detectors which could beimplemented in a wireline tool to assist an operator in interpretinglogs post-fracking by subdividing the neutron detectors into a pluralityof azimuthally arranged detectors, which are in turn shielded within amoderator to infer directionality to incident neutrons and gamma.

U.S. Pat. No. 4,883,956 to Manente et al. discloses an apparatus andmethod for investigation of subsurface earth formations, in particularusing an apparatus adapted for movement through a borehole. Dependingupon the formation characteristic or characteristics to be measured, theapparatus may include a natural or artificial radiation source forirradiating the formations with penetrating radiation such as gammarays, x-rays or neutrons. The light produced by a scintillator inresponse to detected radiation is used to generate a signalrepresentative of at least one characteristic of the radiation and thatsignal is recorded.

U.S. Pat. No. 6,078,867 to Plumb discloses a method for generating athree-dimensional graphical representation of a borehole, comprising thesteps of: receiving caliper data relating to the borehole, generating athree-dimensional wire mesh model of the borehole from the caliper data,and color mapping the three-dimensional wire mesh model from the caliperdata based on either borehole form, rugosity and/or lithology.

SUMMARY

An x-ray-based cased wellbore environment imaging tool is provided, thetool including at least an x-ray source; a radiation shield to definethe output form of the produced x-rays; a direction controllabletwo-dimensional per-pixel collimated imaging detector array;sonde-dependent electronics; and a plurality of tool logic electronicsand PSUs.

A method of using an x-ray-based cased wellbore environment imaging toolto monitor and determine the integrity of materials within wellboreenvironments is also provided, the method including at least the stepsof: producing x-rays in a shaped output; measuring the intensity ofbackscatter x-rays returning from materials surrounding the wellbore;controlling two-dimensional per-pixel collimated imaging detectorarrays; and converting image data from said detectors into consolidatedimages of the wellbore materials.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an x-ray-based casing imaging tool being deployedinto a borehole via wireline conveyance. Regions of interest within thematerials surrounding the borehole are also indicated.

FIG. 2 illustrates one example of an x-ray-based casing imaging tool,arranged so as to enable imaging of the inner-most casing or tubing inaddition to segments of the materials located outside of the casing ortubing.

BRIEF DESCRIPTION OF SEVERAL EXAMPLE EMBODIMENTS

The methods and means described herein for casing integrity evaluationwhile simultaneously imaging equipment/features located immediatelysurrounding the borehole, through x-ray backscatter imaging in a casedwellbore environment, is disclosed in a package so as to not requiredirect physical contact with the well casings (i.e., non-padded). Themethods and means disclosed herein further comprise the use of acombination of collimators, located cylindrically around an X-ray sourcelocated within a non-padded concentrically-located borehole loggingtool, together with a single or plurality of rotatable two dimensionalper-pixel collimated imaging detector array(s) to also be used as theprimary imaging detector(s). The ability to control the viewingdirection of the collimated detectors permits the operator to either logthe tool through the well casing while the detectors rotatedazimuthally, to produce a two dimension helical ribbon backscatter x-rayimage, or to hold the tool stationary as the collimated detector rotatesazimuthally to capture a cylindrical image that can be improved upon‘statically’ (as the detector continues to recapture casing images thatcan be added to the existing image set), and/or to actuate the detectorsuch that a closer inspection of a particular region may be performed bypan-tilt control of the collimated detector.

In one example embodiment, an x-ray-based casing imaging tool [101] isdeployed by wireline conveyance [103. 104] into a cased borehole [102],wherein the well casing or tubing [102] is imaged. The tool is enclosedby a pressure housing that ensures well fluids are maintained outside ofthe housing.

FIG. 2 illustrates a pressure housing [201] that is conveyed through awell casing or tubing [202]. The pressure housing contains an electronicx-ray source [203] configured to produce x-rays panoramically in aconical output, the shape and distribution of said x-ray output isdetermined by the geometry of the collimator [204], which is formed bycreating a non-blocking region of the radiation shielding. The conicalx-ray beam illuminates a cylindrical section of the casing/tubing [205].The radiation scattering from the casing is imaged by a two-dimensionaldetector array [208], which is attached to a per-pixel array collimator[207]. The detector collimator [207] reduces the field of view of eachpixel of the detector array [208] such that each pixel images a distinctand unique section of the illuminated casing/tubing [205]. A motor/servo[209] is used to rotate the detector azimuthally, such that thecollimated detector array images the illuminated ring section of thecasing/tubing [205]. A further detector assembly [210] rotates upon thesame armature but is geometrically configured to image a section of thewellbore that is illuminated by the x-rays but lays outside of the innersurfaces of the tubing/casing [211]. While the motor/servo [209] rotatesthe collimated detector arrays [207, 208, 210], back-scatter images areacquired by the detector of both the casing/tubing and the materialsbehind the casing/tubing. As the tool is being conveyed through thewellbore, the result is a helical ribbon of stacked images, with twodistinct radial depths of investigation.

In a further example embodiment, the deeper depth of radial inspectiondetector assemblies are used to create images of sand-screens, to aidinspection.

In a further example embodiment, the deeper depth of radial inspectiondetector assemblies are used to create images of perforations, to aidinspection.

In a further embodiment still, the deeper depth of radial inspectiondetector assemblies would be used to create images of gravel-packs, toaid inspection.

In another embodiment, as the detector assembly rotates azimuthally,each axial ‘column’ of pixels of the detector arrays are sampled suchthat each column would image a similar section of the casing/tubing thathad been imaged by its neighbor prior during the last sample. Uponencoding the images with the known azimuthal capture position of theimage section, the separate image pixel columns associated with eachimaged ‘slit’ section of the casing/tubing could be summated/averaged toproduce a higher quality image within a single pass.

In yet another embodiment, two detectors are used back-to-back facingoutwards, or side-by-side facing opposite directions, for each detectorset, such that when the detector assembly is rotated, a double-helicalimage ribbon is produced as the tool is conveyed through the wellbore.

In another embodiment, ‘n’ detectors are used facing outwards, orarranged for maximal volumetric packing efficiency, for each detectorassembly position, such that when the detector assembly is rotated,n-helical image ribbons are produced for each radial depth being images,as the tool is conveyed through the wellbore.

In another embodiment, the logging speed and detector assemblyrotational rate are matched such, that a single azimuthal rotation ofthe detector assembly is performed while the tool is conveyed axially byone imaged axial tubing/casing section [9] height, such that theresulting images of the casing/tubing, and the outer layer ‘skin’ iscomplete and helically welded.

In a further embodiment, the detector assemblies' rotation andaxial/radial tilt are controlled through the use of servos/actuatorssuch that the operator may stop the tool within the borehole and inspectcertain sections of the casing/tubing (i.e. without the detectorassembly being in continual rotation mode).

In a further embodiment, the operator can stop the conveyance of thetool and use the azimuthal rotation of the detector assembly tocontinually sample the same images tubing/casing illuminated cylinder[9] section, such that the resulting data set can build/summatestatistically to improve image quality.

In another embodiment, the backscatter images also comprise spectralinformation so that a photo-electric or characteristic-energymeasurement may be taken, and the imaged material analyzed forscale-build up, casing corrosion, etc.

In a further embodiment, machine learning is employed to automaticallyanalyze the spectral (photo electric or characteristic energy) contentof the images to identify key features, such as corrosion, holes,cracks, scratches, and/or scale-buildup.

In a further embodiment, the per-pixel collimated imaging detector arrayfurther comprises a single ‘strip’ array (i.e., one pixel wideazimuthally) and multiple pixels long axially—the imaging result is thena ‘cylindrical’ ribbon image. When the tool is moved axially (either bywireline-winch or with a stroker, for example) and a new image settaken, a section of casing is imaged by stacking cylindrical ribbonimages/logs.

In a further embodiment, machine learning is employed to automaticallyreformat (or re-tesselate) the resulting images, as a function of depthand varying logging speeds or logging steps, such that the finalizedcasing and/or cement image is accurately correlated for azimuthaldirection and axial depth, by comparing with CCL, wireline run-inmeasurements, and/or other pressure/depth data.

The foregoing specification is provided only for illustrative purposes,and is not intended to describe all possible aspects of the presentinvention. While the invention has herein been shown and described indetail with respect to several exemplary embodiments, those of ordinaryskill in the art will appreciate that minor changes to the description,and various other modifications, omissions and additions may also bemade without departing from the spirit or scope thereof.

1. An x-ray-based cased wellbore environment imaging tool, said toolcomprises: an x-ray source; a radiation shield to define the output formof the produced x-rays; a direction controllable two-dimensionalper-pixel collimated imaging detector array; sonde-dependentelectronics; and a plurality of tool logic electronics and PSUs.
 2. Thetool of claim 1, wherein said imaging detector comprises atwo-dimensional per-pixel collimated imaging detector arrays wherein theimaging array is one pixel wide and multiple pixels long.
 3. The tool ofclaim 1, wherein said imaging detectors further comprise two sets oftwo-dimensional per-pixel collimated imaging detector arrays.
 4. Thetool of claim 1, wherein said imaging detectors further comprise aplurality of two-dimensional per-pixel collimated imaging detectorarrays.
 5. The tool of claim 1, wherein the rotation rate of the imagingdetectors is matched to the axial logging speed of said tool so as tocreate a continuous helical image ribbon without blind regions.
 6. Thetool of claim 1, wherein the imaging detectors rotate continuously whilesaid tool is stationary within the wellbore to produce statisticallyaccumulated cylindrical images over the same region of the wellbore. 7.The tool of claim 1, wherein the images further comprise spectralinformation to inform the characteristics of any wellbore materials ordebris.
 8. The tool of claim 1, wherein said shield further comprisestungsten.
 9. The tool of claim 1, wherein the tool is configured so asto permit through-wiring.
 10. The tool of claim 1, wherein the tool iscombinable would other measurement tools comprising one or more ofacoustic or ultrasonic measurement tools.
 11. The tool of claim 1,wherein the tool is used to determine the position, distribution andarea of perforations within the casings surrounding the cased wellbore.12. The tool of claim 1, wherein the tool is used to determine theposition and integrity of sand-screens within the casings surroundingthe cased wellbore.
 13. The tool of claim 1, wherein the tool is used todetermine the position and integrity of gravel-packs within the casingssurrounding the cased wellbore.
 14. The tool of claim 1, wherein thetool is used to determine the position and integrity of side-pocketmandrels within the casings surrounding the cased wellbore.
 15. The toolin claim 1, wherein machine learning is employed to automaticallyreformat or re-tesselate the resulting images as a function of depth andvarying logging speeds or logging steps.
 16. A method of using anx-ray-based cased wellbore environment imaging tool to monitor anddetermine the integrity of materials within wellbore environments, saidmethod comprising: producing x-rays in a shaped output; measuring theintensity of backscatter x-rays returning from materials surrounding thewellbore; controlling two-dimensional per-pixel collimated imagingdetector arrays; and converting image data from said detectors intoconsolidated images of the wellbore materials.
 17. The method of claim16, further comprising using said imaging detector to createtwo-dimensional per-pixel collimated imaging detector arrays wherein theimaging array is one pixel wide and multiple pixels long.
 18. The methodof claim 16, further comprising using said imaging detectors to createtwo sets of two-dimensional per-pixel collimated imaging detectorarrays.
 19. The method of claim 16, further comprising using saidimaging detectors to create a plurality of two-dimensional per-pixelcollimated imaging detector arrays.
 20. The method of claim 16, furthercomprising matching the rotation rate of the imaging detectors to theaxial logging speed of said tool in order to create a continuous helicalimage ribbon without blind regions.
 21. The method of claim 16, furthercomprising continuously rotating the imaging detectors while said toolis stationary within the wellbore in order to produce statisticallyaccumulated cylindrical images over the same region of the wellbore. 22.The method of claim 16, further comprising using spectral information toinform the characteristics of any wellbore materials or debris.
 23. Themethod of claim 16, further comprising forming said shield fromtungsten.
 24. The method of claim 16, further comprising using the toolto determine the position, distribution and area of perforations withinthe casings surrounding the cased wellbore.
 25. The method of claim 16,further comprising using the tool to determine the position andintegrity of sand-screens within the casings surrounding the casedwellbore.
 26. The method of claim 16, further comprising using machinelearning to automatically reformat or re-tesselate the resulting imagesas a function of depth and varying logging speeds or logging steps.